200 mile RF transmitter (and high altitude balloon)

If there is one thing we like, it’s a fellow hacker so enthusiastic about his or her work that they write the article practically for us by including as much detail and information as possible.

In this two part hack, [Scott] wrote in to let us know not only about a high school built high altitude balloon, but also his $5 long range RF transmitter. The former is simply GPS and video data logged over the flight, but [Scott’s] specialty comes in the latter. A 74HC240 octal buffer is using to amplify the signal (Morse code) from an ATTiny44a with a 29MHz oscillator, producing a usable signal as far away as 200 miles.

It is low bandwidth, but if you’re looking for a simple transmitter in your project and need something with more power (and a smaller package), this might be the ticket.

Too bad that under the current 10 meter band plan (1) this freq. calls for CW, phone and image only (no data, though I guess you can convert your output to CW), (2) you have to have a general-class license to use this, and (3) you have to broadcast your call sign every 10 minutes.

But good job nonetheless. For those of you interested, the 1-chip transmitter (or something similar) were available on eBay for about $1 apiece last year (but most of them were general-class units).

The metal square is a “canned oscillator”. Apply voltage (5v) and it magically outputs square waves at the frequency stamped on the top. It’s temperature-compensated, and far more temperature stable than simple oscillator designs (i.e., Colpitts oscillator), which is why I selected it for the flight. In general they’re not really intended for radio transmitters, as they produce odd harmonics out the wazoo. They’re more useful for time-source, counting, and calibration purposes. I was lucky to have one on hand in a HAM band, and being licensed (AJ4VD) it was an easy snap-in choice for this project! In general, it’s not a good idea to use these things for any kind of serious RF transmitter designs.

I’m a dental student at the University of Florida. Go gators! The rest of the students were high school students from around the country who took an introduction to aerospace engineering course at UF (in association with NASA) for AP college credit. The faculty instructors were aerospace engineering grad students at UF. They pulled me into the project at the last minute because they know I’m all about hacking together ultra-cheap (yet surprisingly functional) radio transmitters

Believe it or not the first person to invent radio transceiver was not Marconi nor Tesla. It was a dentist from Washington DC. He invented the first wireless Morse-Code network (7 miles in downtown Wash DC for the government) in 1870’s. Earlier in 1860’s he achieved a 14 mile distance between mountains in Virginia just after the Civil War. He was Dr. Mahlon Loomis.

I just met a guy in my class who’s a Ham operator- I’ll ask him about this. If it carries that far, good chance you have to be a higher level Ham to legally use this.

If you do have to be so, this hack may be the sole reason I become a Ham operator- if I need to be one to use this, I will go get my certification!

I am extremely impressed, though, at how small he made the entire transmitter, especially since it carries for 200 miles! I cannot comprehend how it can be so small and carry that far- I’ve never seen a transmitter this powerful and this small and simple. Very, very impressive.

@Drew – AWESOME! I got my HAM license for this very reason! Radio is such a fun field to hack. I’m still working on the designs of a different project (no circuit diagrams yet intentionally) but if you liked this post, you’ll love these sneak peaks:

~500mW transmitter:
Signal in Belgium:

Note that my “antenna” is just 20ft. of small wire hanging inside my apartment! A little more work, then I’ll write it up with circuit diagrams and try to get it on HAD.

@mike – Good question! Even with the amplifier completely disabled, power to the oscillator produced a loud enough tone to be heard. Rather that trying to decipher Morse code by listening to two different intensities of audio, I chose to completely kill power to the oscillator during the silent portions. This way the students were able to hear very clear Morse code on a portable radio receiver while we worked on the transmitter in the same room (even without the amplifier the audio was overloading the receiver, so turning the amplifier on/off wouldn’t have been as exciting to listen to during development). One of the disadvantages (unexpected perks?) was the loss of frequency stability. Those canned oscillators are rock-stable, but they take half a second or so to warm up. This “warm-up stabilization” can be seen on the image captures http://swharden.com/tmp/balloon/strong.PNG

I will too! I don’t know how hard it is though, I know next to nothing about Ham radio outside using oil pots to dissipate heat, and that really cool project that was able to send computer data over a radio signal- it was used to send medical charts after a power outage or something in my hometown of Pittsburgh- I can’t remember the name. It was like a much more advanced morse code for computer data.

I will check out the links tomorrow, can’t wait to see what else you’re up to. I’ll print out your page and show my friend the ham and see what he says- and post the result here.

@Drew – Feel free to contact me for details. My Gmail is on my website. I’d be more than willing to tell you (and anyone else interested) how to get a HAM license. They’re not hard to get, especially since the question bank is posted online! Just be careful what question bank you study, because questions are changed every 5 years and the entry-level (technician class) exam questions change in August this year I think. My wife got her technician license after ~2 hours of studying. A few months ago her cell phone was damaged (washed with the laundry) and we communicated via 144MHz FM radio for a couple weeks lol… glad we were both licensed! You should look into it. So much fun. Awesome learning. GREAT COMMUNITY!

It’s rockbound (single frequency dep. on crystal), and it’s not amazing, but it’s certainly functional (especially for same-room transmitters lol) and cheap! (a few bucks) It’s far toucher to perfect than a transmitter. For “real” receiving of far-off signals you have to have a perfectly tuned circuit at the fronted to reduce AM radio interference, and maximally pass the signals of your desired frequency requiring some math to get the values for the required inductance / antenna matching / capacitance (variable). I’ve done it (details on those pages above) and only recommend it for tinkering value. There are better (but more expensive) designs out there. Google for “softrock” radio receivers – they’ve got some cool stuff going on!

Great material.
ps too much talk about legality of this, but dont forget that FCC laws are equivalent to claiming ownership of sunlight or criminalizing vocal communication without permit, simply it abuse of everyone birth given rights

“FCC laws are equivalent to claiming ownership of sunlight or criminalizing vocal communication without permit, simply it abuse of everyone birth given rights”

Have a search for ‘tragedy of the commons’ and have a think about what might happen if radio communications were unrestricted. The fact that an organisation might be an unpleasant overbearing bureaucracy with unreasonable demands and expectations does not mean that it isn’t doing a very valuable job.

MY LEGAL RATIONALE – the ‘danger’ of border-line legal radio projects increases with output power. I’m licensed to use 29MHz (license AJ4VD), which I do feel is important. Amateur radio licenses are a good thing, as they do a great job at promoting education. Now, if I were transmitting 50,000 watts in this project, the FCC would probably have a larger axe to grind. However, in this project I’m using about 0.01W (probably less than the a wireless car door unlocker keychain) and since it’s practically undetectable, I’m not overly-concerned.

“think about what might happen if radio communications were unrestricted”
interfering guys get tired of each other and change frequency. Argument about chaos pretty much outdated and apply only to worldwide low-frequency communication, there is plenty local space,for exapmle WIFI prove this with only 14 channels

@therian – Of course microwave frequencies are wide open for the taking. Use them all you want and no one will compete with you …how many hundred miles do you think you can send a message on the ~2GHz wifi frequencies? There are advantages to low frequencies (i.e., sending messages around the globe with milliwatts at the expense of bitrate), and there is very limited bandwidth down there, and thus the ability to regulate its usage is necessary.

“ps too much talk about legality of this, dont forget that FCC laws are equivalent to claiming ownership of sunlight or criminalizing vocal communication without permit”

Bad analogy.

No matter how you choose to use sunlight on your property, nothing you do will prevent me from being able to use it, too. On the other hand, your abuse of RF spectrum space can deny me my rights to use it, too.

Even a malfunctioning street lamp or a cracked insulator on a power pole, for example, has rendered large chunks of the lower HF ham bands unusable. I know, because when it happened locally, I used test equipment to pinpoint the sources of this unintended radiation and then worked with property owners and the power company to rectify those problems. These people acted in a responsible fashion.

As to the matter of vocal communication, if you think there are no rules that govern it, try yelling “fire” in a movie theater or make a joke about a bomb while you are standing in line at an airport. I can guarantee that you will be contacted by someone with a badge who will be more than happy to explain to you why you *don’t* have the right to do those things.

If there is too much talk of anything, there is too much talk of “rights” without any acknowledgement of “responsibility.” Adults recognize that rights and responsibility go together, and are inseparable. Adolescents think they are entitled to use the credit card without having to pay the bill.

@scott couldn’t you use this to create an automatic tracking system for the 900mhz directional antenna?
If you sent the gps data by CW using your radio You could calculate the location to point the 900mhz antenna using some servos.
You could also slave a camera to it for imaging of the balloon.
Just a though.

I talked to my friend, he wasn’t able to give me a clear answer since he didn’t have time to read the article I printed for him yet.

I did my own research- it seems the lowest level, Amateur Technician class, can use SSB(Phone)& CW (continuous wave) in the band of 28.300 – 28.500 Mhz, which is roughly 10 meters, and the range your project works in. I don’t know anything yet, so I’m not sure if the signal your transmitter is sending out is one of those signal types.

Thanks very much for offering to answer questions via email, I will take you up on that this weekend- my weekdays are insanely busy- I’m fortunate enough to be learning machining, welding, electronics, and OSHA training at my local college in an experimental manufacturing boot camp of sorts, and I’m meeting people into all kinds of cool Hackaday type backgrounds other than my machining background.

Two last questions here though:

1. What is the signal this uses called? I know it’s using Morse code, but what signal type is that? “CW”, “SSB”, or something else?

2. Would a reciever for this be possible to be nearly as small? I’d like to control an RC plane for 200 miles shooting landscape photos on mountaintops.

@lwatcdr – no need to use the 900mhz dish. I’d just send GPS data directly using FSK (frequency shift keying) to send the coordinates. Having a microcontroller send RTTY (radio teletype) also seems easy! There are so many possibilities…

@Drew – I can see you’ve got a lot of energy! That’s awesome. In a nutshell:

1.) Don’t limit yourself to the lowest radio amateur license (“technician”). Yeah it’s a start, but go ahead and get the 2nd level (“general”), then you can use any amateur band (the lower regions of which are reserved for the highest-level licensees) and have the whole spectrum at your fingertips.

2.) Begin reviewing the material to get your radio license. You’ll learn about all the operating modes (SSB, FM, AM, CW), frequencies, and much more! It’ll give you a better idea of what’s used for what and why, such as why video is best sent on higher frequencies (i.e., 900MHz) and why *continuous wave* (CW) like what I used in this project is so good for low power transmission of Morse code!

3.) Controlling an RC plane 200 miles away would definitely require something more sophisticated, but not outside the realm of hobbyists! Again, read the exam prep material! IMHO the best way is to read the question bank and Google why an answer is what it is if you don’t get it.

4.) depending on where you live, you probably have an active VHF repeater within range. Think of it as an IRC server for local radio operators. Once you get on the air with an inexpensive VHF radio (I started with a $65 Puxing 777 from eBay) you’ll meet a lot of people on the air who can help you learn a ton just by talking to them, and probably even let you borrow equipment of your own until you know what you want to buy! Similar to how computer gurus have tons of old computers in a closet somewhere, a lot of radio gurus have tons of old equipment they’d be happy to lend out to an eager learner!

Get that license and make some contacts =o)

Once you have a working knowledge of major RF concepts, the world is yours for the hacking!

@scott
What I was suggesting was to use your system to send the GPS signal to a ground station that would then use that date to point the 900mhz dish. That way if you lost the connection with the 900mhz for some reason it might be possible to reacquire the signal with little effort.
All you would need on the ground station is a GPS module and a compass module. You could even mount it on a car or pickup truck and have a mobile ground station.
I have been thinking of doing something like that with a wifi data link using an old echostar dish. The problem I had was if for some reason the dish lost lock it would have a hard time getting it back. With your transmitter I would have a good long range data source to use for dish pointing.

Sorry to resurrect this thread but I happned to come across this hack and find it very interesting. Im doing a HAB project with my kids (Im about a year behind schedule), hopefully we will be launching 4/17. I’ve been looking for a backup transmitter and think this will work just fine. How did you program the ATtiny chip?

I plan to use msp430 launchpad utilizing QRSS cw beacon firmware..forget the LED’s..save power and weight…using the free energia programming software its like programming an arduino..as a matter of fact porting exisiting arduino code to msp430 is easy

Using QRSS techniques, really slow morse code, where the dits are several seconds long, and QRSS DSP/FFT software processing the static you ‘hear’ at that frequency, this transmitter can be heard globally…nice project..listen for my upcomming ‘pico balloon’ launches this summer